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From: Daniel Phillips <phillips@arcor.de>
To: Andrew Morton <akpm@digeo.com>, imran.badr@cavium.com
Subject: Re: Calculating kernel logical address ..
Date: Mon, 9 Sep 2002 20:23:04 +0200
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On Monday 09 September 2002 20:08, Andrew Morton wrote:
> Imran Badr wrote:
> > 
> > The virt_to_bus() macro would work only for kernel logical addresses. I am
> > trying to find a portable way to figure out the kernel logical address of a
> > user buffer so that I could use virt_to_bus() for DMA. The user address is
> > mmap'ed from kmalloc'ed buffer in the mmap() entry of my driver. Now when
> > the user wants to send this data to the PCI device, it makes an ioctl call
> > and give the user address to the driver. Now driver has to figure out the
> > kernel logical address for DMA.
> 
> You can obtain this info by walking the user's pagetables with
> get_user_pages().  That give `struct page' pointers, with which
> all things are possible.

As long as you can be sure they won't spontaneously vanish on you.

-- 
Daniel
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